Senior Member

it's widely known that for most lenses, it's essential to stop down the lens 2-3 stops from their widest aperture. i.e. f/2.8 sharpest around f/5.6.

if i use a teleconverter (2x) with a f/2.8 glass, the effective aperture is now f/5.6. does that mean the lens is already at its sharpest aperture ? or do i still have to stop down 2 stops to get the sharpest image ?